Saline and warm Mediterranean water flowing through the Bosporus Strait maintains a permanent pycnocline with vertical separation of oxic (O(2)), suboxic (absence of O(2) and H(2)S), and anoxic (H(2)S) zones in the Black Sea. The stable suboxic zone implies restricted vertical mixing of the upper oxic and lower anoxic layers and limited vertical flux of oxygen that cannot balance the upward flux of sulfide. We report data that directly confirm massive lateral injections (>200 km from the Bosporus) of oxygen-enriched waters of the Bosporus plume, created by the mixing of shallow, cold, intermediate-layer Black Sea water with Mediterranean water. These plume waters are laterally injected into the oxic layer and, more importantly, into the suboxic and anoxic layers over several small vertical scales ("fingers" of similar to5 m) at water densities (sigma(1)) from 15.0 to 16.4. O(2) injection oxidizes Mn(II) to Mn(III,IV), which then oxidizes H(2)S. The onset of H(2)S detection occurs in deeper waters in the southwest (>170 m; sigma(1) approximate to 16.4) relative to the west central Black Sea (110 m; sigma(1) approximate to 16.2) and coincides with increased MnO(2) and S(8) formation in the southwest.